Method for operating a drivetrain

Abstract

A method for operating a drivetrain of a motor vehicle including a hybrid drive with a combustion engine and an electric motor. A transmission is arranged between the hybrid drive and a drive output and a clutch is arranged between the combustion engine and the electric motor so that, if a failure occurs in the drivetrain, especially in a transmission control device of the transmission, a gear corresponding to an emergency gear is engaged or remains engaged in the transmission. When the emergency gear is engaged, the motor vehicle is in motion and the engine speed falls below a defined value, the clutch arranged between the combustion engine and the electric motor disengages.

1. A method for operating a drivetrain of a vehicle in which the drivetrain comprises a hybrid drive comprising a combustion engine ( 2 ) and an electric motor ( 3 ) with a transmission being arranged between the hybrid drive and a drive output ( 6 ), and a clutch ( 4 ) being arranged between and directly connecting the combustion engine ( 2 ) with the electric motor ( 3 ) such that, if a fault occurs in the drivetrain, a gear corresponding to an emergency gear is one of engaged or retained in engagement in the transmission ( 5 ) and the combustion engine can supply drive to the electric motor ( 3 ) without driving the drive output ( 6 ), the method comprising the steps of:
 upon detecting a fault in the drivetrain, one of engaging and retaining the emergency gear; and 
 with the emergency gear engaged, if the vehicle is driving and an engine speed falls below a defined value, then disengaging the clutch ( 4 ), arranged directly between the combustion engine ( 2 ) and the electric motor ( 3 ) so as to avoid stalling of the combustion engine ( 2 ) and assist with subsequently restarting and travel of the vehicle. 
 
     
     
       2. The method according to  claim 1 , further comprising the step of using an idling speed of the combustion engine ( 2 ) as the defined value; and
 upon stopping the vehicle, restarting and commencing further travel of the vehicle with the emergency gear engaged and with the clutch ( 4 ) still disengaged solely by utilizing drive from the electric motor ( 3 ) and supplying hydraulic pressure for retaining engagement of the emergency gear by electrically driving an auxilliary hydraulic pump via a pump motor. 
 
     
     
       3. The method according to  claim 1 , further comprising the step of restarting the vehicle when the emergency gear is engaged, after the vehicle has come to a stop, with the electric motor ( 3 ) while the clutch ( 4 ), arranged between the combustion engine ( 2 ) and the electric motor ( 3 ), remains disengaged. 
     
     
       4. The method according to  claim 3 , further comprising the step of providing hydraulic pressure, required for retaining engagement of the emergency gear via an auxiliary hydraulic pump driven by an electric motor, when restarting the vehicle. 
     
     
       5. The method according to  claim 4 , further comprising the step of switching off the auxiliary hydraulic pump and providing the hydraulic pressure by a main hydraulic pump driven by a drive input shaft, when the engine speed exceeds a defined value. 
     
     
       6. The method according to any of  claim 3 , further comprising the step of engaging the clutch ( 4 ), between the combustion engine ( 2 ) and the electric motor ( 3 ), to start the combustion engine ( 2 ) after restarting the vehicle in the engaged emergency gear and once the electric motor ( 3 ) speed exceeds a defined value. 
     
     
       7. The method according to  claim 6 , further comprising the step of engaging the clutch ( 4 ), between the combustion engine ( 2 ) and the electric motor ( 3 ), to start the combustion engine ( 2 ) when the electric motor ( 3 ) speed exceeds an idling speed of the combustion engine ( 2 ). 
     
     
       8. The method according to  claim 1 , further comprising the step of, with the emergency gear engaged, a driver's wish for a traction force interruption is indicated either by moving a selector lever to one of a P position or a N position, while the vehicle is at rest, or to the N position while the vehicle is driving, and disengaging a friction element, arranged between the electric motor ( 3 ) and the drive output ( 6 ), and engaging the clutch ( 4 ) between the combustion engine ( 2 ) and the electric motor ( 3 ) so that when a traction force is interrupted, the combustion engine ( 2 ) will be started and a battery charged. 
     
     
       9. The method according to  claim 8 , further comprising the step of disengaging a clutch or a brake as a transmission-internal friction element. 
     
     
       10. The method according to  claim 8 , further comprising the step of disengaging a clutch ( 8 ) as a transmission-external friction element. 
     
     
       11. The method according to  claim 1 , further comprising the step of coupling the combustion engine ( 2 ) to the electric motor ( 3 ) without coupling the electric motor ( 3 ) to the transmission ( 5 ). 
     
     
       12. The method according to  claim 1 , further comprising the step of supplying torque to the combustion engine ( 2 ) from the electric motor ( 3 ) without supplying torque to the transmission ( 5 ). 
     
     
       13. The method according to  claim 1 , further comprising the step of arranging the electric motor ( 3 ) between the combustion engine ( 2 ) and the transmission ( 5 ). 
     
     
       14. A method of operating a drivetrain of a vehicle, the drivetrain comprising a hybrid drive comprising a combustion engine and an electric motor ( 3 ) with a transmission ( 5 ) being arranged between the hybrid drive and a drive output ( 6 ) and a clutch ( 4 ) directly connecting the combustion engine ( 2 ) to the electric motor ( 3 ) such that the combustion engine can supply drive to the electric motor ( 3 ) without driving the drive output ( 6 ), and if a fault occurs in the drivetrain, a gear corresponding to an emergency gear is one of engaged or retained in engagement within the transmission, the method comprising the step of:
 upon detecting a fault occurring within the drivetrain, one of engaging and retaining the emergency gear; 
 with the emergency gear engaged, if the vehicle is driving and an engine speed falls below a defined value, then disengaging the clutch ( 4 ), arranged between the combustion engine ( 2 ) and the electric motor ( 3 ), so as to avoid stalling of the combustion engine and thereafter assist with subsequently restarting and travel of the vehicle; and 
 once the vehicle stops, restarting and commencing further travel of the vehicle with the emergency gear engaged and with the clutch ( 4 ) still disengaged solely by utilizing drive from the electric motor ( 3 ) and supplying hydraulic pressure for retaining engagement of the emergency gear by electrically driving an auxiliary hydraulic pump via a pump motor. 
 
     
     
       15. A method of operating a drivetrain of a vehicle, the drivetrain comprising a hybrid drive comprising a combustion engine and an electric motor ( 3 ) with a transmission ( 5 ) being arranged between the hybrid drive and a drive output ( 6 ) and a clutch ( 4 ) directly connecting the combustion engine ( 2 ) to the electric motor ( 3 ) such that the combustion engine can supply drive to the electric motor ( 3 ) without driving the drive output ( 6 ), and if a fault occurs in the drivetrain, a gear corresponding to an emergency gear is one of engaged or retained in engagement within the transmission, the method comprising the step of:
 upon detecting a fault occurring within the drivetrain, one of engaging and retaining the emergency gear; 
 with the emergency gear engaged, if the vehicle is driving and an engine speed falls below a defined value, then disengaging the clutch ( 4 ), arranged between the combustion engine ( 2 ) and the electric motor ( 3 ), so as to avoid stalling of the combustion engine ( 2 ) and assist with subsequently restarting and travel of the vehicle; 
 once the vehicle stops, restarting the vehicle with the emergency gear engaged with the clutch ( 4 ) still disengaged solely by utilizing drive from the electric motor ( 3 ) and supplying hydraulic pressure for retaining engagement of the emergency gear by electrically driving an auxiliary hydraulic pump via a pump electric motor; 
 after a defined speed of the electric machine ( 3 ) is exceeded, switching off the auxiliary hydraulic pump and then using hydraulic pressure, supplied by a main hydraulic pump driven by a drive input shaft for retaining engagement of the emergency gear; and 
 once a speed of the electric machine increases at least above an idling speed of the combustion engine ( 2 ), reengaging the clutch ( 4 ) arranged between the combustion engine ( 2 ) and the electric motor ( 3 ) in order for starting the combustion engine ( 2 ). 
 
     
     
       16. The method according to  claim 15 , further comprising the step of, with the emergency gear engaged, a driver's wish for a traction force interruption is indicated either by moving a selector lever to positions P or N, while the vehicle is at rest, or to position N while the vehicle is driving, and disengaging a friction element, arranged between the electric motor ( 3 ) and the drive output ( 6 ), and engaging the clutch ( 4 ) between the combustion engine ( 2 ) and the electric motor ( 3 ) so that when a traction force is interrupted, the combustion engine ( 2 ) will be started and a battery charged. 
     
     
       17. The method according to  claim 14 , further comprising the step of directly connecting the electric motor ( 3 ) to the transmission ( 4 ) via another clutch ( 8 ). 
     
     
       18. The method according to  claim 15 , further comprising the step of directly connecting the electric motor ( 3 ) to the transmission ( 4 ) via another clutch ( 8 ).